Oxidation-inhibited lubricating compositions



Patented Oct.- 26,

OXIDATION -INHIBITED LUBRICATIN G COMPOSITIONS Herman D. Kluge andJohnA. Patterson, Wappingers Falls, N. Y

., asslgnors to The Texas Company, New York, N. Y., a corporation ofDelaware No Drawing. Application November 30, 1945, Serial No. 632,106.In Canada December 2, 1944 7'Clalms. 1.

This invention relates to an improved lubricating composition possessingenhanced oxidationresistant properties, and particularly to lubricatingcompositions containing the combination of an oxidation inhibitor and anoil-miscible dicarboxylic acid.

This is a. continuation-in-part of copending application, Serial No.519,812, filed Jan. 26, 1944,"

now abandoned.

The hydrocarbon oils used in lubricating compositions are usuallysubject to deterioration caused by heat and aeration resulting from theconditions of operation of the lubricant. This deteriorationor-oxidation causes the formation of acidic and sludge-like bodies whichattack the bearing metals and deposit carbonaceous films on the surfacesto be lubricated. The resistance of the hydrocarbon oil and/orlubrtating composition to deterioration or oxidation is a measure of thelubricating value of the oil or composition in service and is a definitecriterion of the service life' of the lubricant. This resistance hasbeen materially increased by the incorporation of small amounts ofso-called oxidation inhibitors which, in eifect, retard or minimize theformation of the acidic and sludge-like bodies in the oil for anextended period of time, depending upon the type of inhibitor. 1

However, increased demands on the performance of mechanical equipmenthave necessitated an improvement in the lubricants with which theequipment is lubricated in such a manner as to provide safe lubricationover longer service periods and undermore stringent operatingconditions. This problem of improving a, lubricant so as to increase theservice life cannot be solved by the simple expedient of increasing theamount of oxidation inhibitor in the lubricant since'the majority ofinhibitors possess an optimum concentration above which no furtherimprovement in resistance is noted. Also, the further incorporation of asecond oxidation inhibitor does not necessarily improve theoxidation-resistant properties since it is recognized that these typesof inhibitors are not generally compatible with one another, and as arule do not cooperate to produce an additive eifect.

It has been found that, by incorporating a small amount of anoil-miscible dicarboxylic acid in a lubricating composition which isinhibited against oxidation in the presence of water, or byincorporating a combination of an oil-miscible dicarboxylic acid and anoxidation inhibitor possessing anti-oxidant properties in the presenceof water into a lubricating composition, a lubricant is obtained whoseoxidatiomresistant properties are materially greater than thoseresulting from the oxidation inhibitor alone.

Although the invention is broadly applicable to all oxidation inhibitorscapable of functioning as such in the presence of water, it isparticularly applied to the oxidation inhibitors falling within theclassification of diamino diaryl alkanes together with substitutedderivatives thereof. In general, the oxidation inhibitors which functionas such in the presence of waterare those which are usually waterinsoluble and resistant to hydrolysis or decomposition in the presenceof water.

As previously mentioned, the inhibitors generally possess anoptimumconcentration when incorporated in hydrocarbon oils orlubricating compositions, and this optimum concentration is dependentupon the type of inhibitor, the type of .'base oil, and the conditionsof operation of the lubricant. These concentrations usually vary withinthe range of Mil-5.0% by weight and, in most instances, between 0.12.0%by weight;

According to the invention it has been discovered that the combinationof an oil-miscible dicarboxylic acid and an oxidation inhibitor,preferably a diaminodiaryl alkane, when incorporated in a minerallubricating oil provides a lubricating composition whose resistance tooxidation is materially greater than that obtained by the addition ofthe oxidation inhibitor itself.

It is to be understood that the sequence of incorporation of theinhibitor and dicarboxylic acid is not a limitation of the invention andde-.

pends only upon the practical aspects of the compounding ofthelubricant. In other words, aconcentrate of the combination of thedicarboxylic acid and inhibitor may be incorporated in the base oil orthe dicarboxylic acid may be separately incorporated in a previouslyprepared oxidation-inhibited lubricant.

The oil-miscible dicarboxylic acids of the invention may be anyaliphatic dicarboxylic acid which contains at least 10 carbon atoms inthe molecule and at least one carbon atom between the carboxyl groups.

All dicarboxylic acids are subject to classification in either of twogroups: (1) dicarboxylic acids which possess a fixed configuration; and

(2) dicarboxylicacids which exist in stereo-isomeric form. For thepurposes of the present invention it has been found preferable to selectan oil-miscible dicarboxylic acid whose carboxyl groups are in a planesymmetrical configuration. Typical examples of the types of acidsfalling 'droxide in 200 cos. of water within this preferredclassification are the alkyl maleic acids, alkyl succinic acids. andalkyl citraconic acids.

The amounts in which the dlcarboxylic acids are incorporated in anoxidation-inhibited lubricating composition, or combined with anoxidation inhibitor and then incorporated in a lubricant, will 'vary inaccordance with the type of inhibitor and the lubricating oil to whichthey are added. In general, the dicarboxylic acid is incorporated in-thelubricating oil in amounts ranging between 0.005%- In certain types ofoil whose specifications include a maximum neutralization number, suchas in turbine oil, the amounts of the acid incorporated will necessarilyhave to be quite small. However, in the other lubricating oils orcompositions where the neutralization number is not a serious factor andperformance is the sole consideration, greater amounts of the acid maybe employed.

As an example of the type of dicarboxylic acids contemplated by theinvention, the following description of and test data on alkyl maleicacid are presented.

The preparation of the alkyl maleic acids is carried out by condensationof maleic acid anhydride with an olefin or mixtures thereof, eitherstraight or branched chain which contains an average of at least 6carbon atoms and preferably 10 or more. These olefins may be obtainedfrom any of the usual sources, such as vapor phase cracking of petroleumoil or wax, or the polymerization of lower molecular weight olefins.This condensation reaction, followed by hydrolysis, producesdicarboxylic acids which mayexist as an alkyl maleic acid, an alkenylsuccinic acid, or mixtures thereof. In order to simplify the descriptionof the acids produced by this reaction, reference will be madethroughout the specification and claims to 'alkyl maleic acids.

The oxidation-resistant properties of the lubricating compositionsprepared in accordance with the invention are illustrated by oxidationtests conducted on a lubricating oil containing an alkyl maleic acidanda representative diamino diaryl alkane. The alkyl maleic acid used inthe oxidation test was prepared asiollows:

Two hundred ninety-seven grams of a poly"- mer gasoline distillate,boiling point 392-450" F., and,68.7 grams of maleic acid anhydride wereheated with stirring at 356 F. for five hours. After cooling thereaction mixture to room temperature, a solution of 80 grams of sodiumbywas introduced. The mixture was heated for one hour at a gentle refluxand thereafter cooled and filtered. The filtered solid was thendissolved in alcohol and water, filtered and evaporated on a steam bath.The residue was acidified with dilute hydrochloric acid, extracted withbenzene, and the benzene solution washed with water until the aqueouslayer was neutral to litmus. The benzene solution was then filtered andthe solvent removed by heating on the steam bath. Neutralization No.209.9.

The oxidation test employed herein is recognized as theproposed ASTMoxidation test for turbine oils.

In this test 300 cos. of the oil sample are introduced to an oxidationcell in which is suspended spiral coils of iron and cODper wire, and 60ccs. of distilled water are added. Oxygen is introduced through afritted glass outlet into the oxidation cell at the rate -of 3liters'per hour.

and 3.0% by weight.

The oxidation cell is suspended in a heated oil bath and the temperaturein the oxidation cell is 485-515 SaYbolt Universal at F.

Oxidation test Hrs. to 2.0 Neut. No. Reference 011 65-72 Reference oil#0.1% tetramethyidiamino diphenyl methane 174-200 Reference 011 #0.1%alkyl maleic acid 230-250 Reference oil 410.1% tetramethyldiaminodiphenyl methane #01 alkyl maleic acid 830 It may be seen from theresults obtained that the oxidation-resistant properties of an oilcontaining recognized oxidation inhibitors are substantially improveCLbythe addition of an oilmiscible dicarboxylic acid such as an alkyl maleicacid.

Additional test results have indicated that oils inhibited with otherwell-known oxidation inhib itors falling within the generalclassification of diamino diaryi alkanes may also be improved by theincorporation of an oil-miscible dicarboxylic acid, and particularly onewhose carboxyl groups are arranged in a plane symmetrical configurartion, as, for instance, alkyl maleic acid. The

following are a few of the specific oxidation inhibitors whose resistantproperties may be improved in accordance with the present invention:

Tetraethyldiamino diphenyl methane Diisoamyldiamino diphenyl methaneTetraamyldiamino diphenyl methane Dlmethyldiamino diphenyl nethaneTetramethyldiamino diphenyi ethane Obviously, many modifications andvariations of the invention, as hereinbefore set forth, may be madewithout departing from the spirit and scope thereof and therefore onlysuch limitations should-be imposed as are indicated in the appendedolaims.

We claim:

1. A lubricating composition comprising a mineral lubricating oil as themajor constituent, about 0.005-3.0% by weight of an oilmiscible alkylmaleic acid having at least 10 carbon atoms in the molecule, and about0.0l-5.0% by weight of an alkyl substituted diamino diphenyl alkane,wherein the said alkyl substituent contains from 1 to 5 carbon atoms andthe said alkane is selected from the group consisting of methane andethane.

2. A lubricating composition according to claim 1, wherein the alkylmaleic acid is a hydrolyzed condensation product of maleic acidanhydride with an olefin containing at least 6 carbon atoms in themolecule.

3. A lubricating composition according to claim 2, wherein the saidalkyl substituted diamino diphenyi alkane is a polyalkyl diaminodiphenyl methane.

4. A lubricating composition according to claim 3, wherein the saidpolyalkyi diamino diphenyl methane is tetramethyi diamino diphenyimethane.

having superioranti-oxidant properties in the presence of water 5. Alubricating composition resistant to ondation in the presence of watercomprising a hydrocarbon oil normally subject to oxidation as the majorconstituent, about 0.005-3.0% by weight of an oil-miscible aliphaticdicarboxylic acid having at least 10 carbon atoms in the molecule andwhose carboxyl groups are in a plane symmetrical configuration, saidacid consistin of the elements carbon, hydrogen and oxygen and beingfree from ether linkages, and about 0.01-5.0% by weight of an alkylsubstituted diamino diphenyl alkane, wherein the said alkyl substituentgroup contains from 1 to 5 carbon atoms and the said alkane is selectedfrom the group consisting of methane and ethane, said dicarboxylic acidand said alkane compound flle of this patent:

being of such character and used in such proporeating composition of analkyl substituted diamino diphenyl methane, and about 0.005-3.0% byweight of an oil-miscible dic'arboxyl ic acid having at least 10 carbonatoms in themolecule and a plane symmetrical configuration.

' HERMAN D. KIiUGE.

JOHN A. PATTERSON.

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